1. Field of the Invention
This invention relates generally to hand-held navigation instruments and particularly to sextants. Most particularly, the invention relates to an apparatus attached to a sextant permitting consecutive instantaneous readings of angle and time of sighting and storage of these readings without separate manual recordation after each sighting.
2. Description of the Prior Art
Modern sextants are changed very little in their mechanical design and use from those used by early mariners. Traditionally, it is a hand-held, quadrant-shaped frame with an arm rotatably connected to the center of the quadrant circle and fastenable around the circumference of the circle which is graduated in degrees, minutes, and seconds. Cooperating with the arm to generate an elevation angle is a tiltable mirror allowing the sextant operator to bring the reflected image of a sighted celestial body into coincidence with the sight line of the horizon. The sextant, held to the eye while sighting the body, is then lowered and the angle of arm rotation required to achieve coincidence is read from the circle. The time at which the sighting occurred is also recorded with the sighted elevation angle for future computations.
The recommended procedure for maximum accuracy when using a sextant is to take sightings of at least three celestial bodies and preferably at least five sightings of each body. Generally, lighting conditions are very poor and the craft upon which the operator is located is moving in pitch, roll, and yaw. Further, the sighted object may be subject to obscuration by fog, clouds, etc. and during the angle/time recordation process it may disappear prohibiting further sightings or, if faint, it may be overloaded and another faint body mistakenly recorded upon subsequent sightings. Thus, even with a helper to record angle/time measurements, sextant operation is frequently crude, awkward and inaccurate. The instant invention is directed to providing accurate multiple angle/time sighting data without repositioning and recordation error.
An additional source of error common to all prior and conventional sextants is the manner in which the sighting angle is generated and measured. Amount of rotation of the shaft to which the pivot arm is affixed is the sole measure of elevation or sighting angle. The angle is sometimes read directly from the indicia marked on the quadrant circumference. In other embodiments, a gear reduction system connected to the shaft displays the generated angle elsewhere on the sextant or on some remote display device. The accuracy of such gear reduction systems, however, is dependent upon the coupling tolerances of the numerous gears, moisture, temperature and the like. More direct and more accurate means not subject to these sources of error are available and the instant invention is further directed to employment of these unique angle generator means.
Yet another source of error common to all conventional sextants is the method by which time data is provided and recorded with the angle data. Most time data is taken from a timepiece separate from the sextant and read after the sighting angle is taken. Some sextants provide a timepiece on the sextant but the sextant must still be taken from the eye after each sighting and serial readings of elevation angle and time taken. The instant invention is yet further directed to providing time recordation simultaneous with angle recordation.